65 L79 overheating, driving me nuts

[Norris W.]

Earlier in the year I purchased a very original (one repaint over 40 years ago) '65 L79 coupe from a friend. He owned the car since the early 80's and parked it inside in about 2000. He was in the "I'm gonna' get it running again for at least 10 years and did some stuff like radiator, carb, etc. Unfortunately he chose an aftermarket radiator rather than DeWitts and I'm HOPING that's the problem. When I got it the radiator had never been wet, although it was installed in the car and hooked up. After replacing the fuel tank, blowing out the lines, rebuilding the fuel pump and carb I put water in it and cranked it, with the thermostat removed in favor of a restrictor washer with a hole about the size of an open thermostat. It ran very warm in a relatively short trip around the neighborhood, so I pulled the water pump and built it as it was leaking. So around the neighborhood again and still hot. I pulled the water pump and put a NEW replacement on it, going to a lot of trouble to make it look like it DID NOT have the reducer bushing for the bypass fitting. Also put on a new fan clutch, sourced from my favorite Corvette parts vendor. Around the neighborhood again, and still almost pegged gauge. Shot the intake right by the thermostat housing and it was showing 225, so replacement sender strikes again BUT it's still hot. Draining the now 50/50 water/anti freeze mix for about the 4th time it is still very black after only running for a few minutes. I'm accustomed to seeing rusty colored coolant, but not black. I should mention that after the first try and with the original waterpump off I made a water hose adapter to replace the thermostat housing and flushed water though it, running out the holes where the waterpump would mount for about 30 minutes BUT it still looks black and nasty under the thermostat. Honestly I don't have an engine removal, scatter and clean out in me at this time with all the other cars I've got scattered. I don't see a name on the radiator, but it's aluminum and the top of it looks as close to correct as any aftermarket one I've ever seen and it takes looking down the sides to see that it's not original configuration. I'm HOPING that it's just not adequate to cool the car and putting a Dewitts in will solve the problem, but common sense tells me that it hasn't been real hot lately, and the drives have been in the 30 to 40 MPH range with no stopping or idling, so I'm not optimistic. I would LOVE suggestions before it goes in the back of the building while I get less aggravating stuff done. Incidentally, the oil looks great and I pumped it up after the new water pump and it held 15lbs overnight. The only thing I'm seeing is this black colored coolant.

[Mark E.]

Re: 65 L79 overheating, driving me nuts

It's hard to diagnose this remotely, but a couple of suggestions:

- Have you used a chemical flush? Flushing with water only doesn't remove rust and sludge very well (the black you're seeing may be oxidation of aluminum).
I recommend "Evapo-Rust Thermocure Coolant System Rust Remover". It's water-based and non-corrosive yet very effective at cleaning the system.

- Remove the restrictor and use a thermostat

- Test the cap

- Check ignition timing and make sure VAC works. Off spec timing is aq common cause of over heating.

[Duke W.]

Re: 65 L79 overheating, driving me nuts

I have a difficult time reading nearly half a screen of single spaced text. It would be much easier for me if you could use the edit function and break it up to a handful of paragraphs. Just hit the return key twice at the end of any sentence.

Duke

[Norris W.]

Re: 65 L79 overheating, driving me nuts

Odd request, but edited as you wish. Hope that means you'll offer some helpful advice.

[Mike T.]

Re: 65 L79 overheating, driving me nuts

Norris - Can you elaborate as to what your friend did to the engine prior to your purchase? You mentioned he was 'going to get it running', did that include engine work? I use DeWitts Radiators in all my Corvettes but there might be something else going on here so before you take the plunge and possibly replace a decent functioning radiator, maybe use a Block Tester kit to determine if by chance you have some combustion gases escaping into the coolant. Since you have a smallblock, there's typically enough gap between the coolant surface and the expansion tank neck, which they recommend to minimize coolant splash. The coolant does have to be up to operating temp when you use it. Engine running, fill vial with Blue Liquid, place down into the neck of the expansion tank, use the squeeze bulb to draw vapors up through the vial of blue liquid for about a minute. Shut off the engine, wait about a minute or two and if you see the blue turning any shade of yellow or green, that's an indicator of combustion gases. Maybe from a crack, maybe from a compromised head gasket. Combustion Gas Tester.jpg

[Norris W.]

Re: 65 L79 overheating, driving me nuts

Mike, the previous owner used it for daily transportation for almost 20 years, until around 2000/2001. I don't recall why he quit driving it, maybe brakes. He's local and a friend who I've known for 40 years or longer. I've always wanted the car and he agreed to sell it to me.

He had bought a battery, changed the oil and I THINK put a kit in the carb, but hadn't tried to crank it and hadn't put coolant in it since installing the new radiator. I trailered it home, looked in the gas tank and YUCK. So bought a tank, etc, etc, primed the oil pump, did brakes, put 50/50 anti freeze in it and cranked it. I wish I had flushed the block thoroughly before cranking, and MAYBE junk from the block has plugged the radiator.

IF I had combustion in the coolant wouldn't I see bubbles in the expansion tank? I did pump it up with a pressure tester and it held pressure overnight (that was before the weekend's latest run hot episode). The blackness of the coolant does make me wonder about your combustion in the coolant suggestion maybe being the problem BUT the overheat is so immediate I would guess it would take longer since coolant level is still the same AND it's NOT making oil or any other indication of water in oil. I've got a BUNCH of big and smallblock Chevy stuff and have always done my own engines, but this one has me buffaloe'd.

[Mike T.]

Re: 65 L79 overheating, driving me nuts

Norris - the black color of the coolant has me scratching my head too. Besides my own vehicles...when I was questioning a heat up issue, I've used it on friends cars and have seen it turn yellow, mostly due to a compromised head gasket. On those that failed the blue liquid test, I did not see any noticeable bubbles in the coolant. On my 66 L79 Coupe, back in the early 90's, I was assembling the 327 and decided to go a little light on the head bolt torques, not sure why, maybe I was concerned about reusing the GM head bolts...that were cleaned and looked okay but back to the story. The 63 Service Manual specifies 60-70. I suspect I went a tad bit low on the torque specs and when I got the car out on the road, mostly okay until I came to a stop and man did that temp gauge needle move quickly. Found no coolant in the oil but it failed the blue liquid test so pulled the heads, new head gaskets, retorqued to roughly 65 pounds and it's been fine ever since.

[Dave P.]

Re: 65 L79 overheating, driving me nuts

and MAYBE junk from the block has plugged the radiator.

^^ This is a distinct possibility. ^^

You have an infrared thermometer. Shoot the radiator inlet and outlet temperatures.

[Norris W.]

Re: 65 L79 overheating, driving me nuts

^^ This is a distinct possibility. ^^

You have an infrared thermometer. Shoot the radiator inlet and outlet temperatures.

That is an excellent suggestion that I wish I'd thought of. I've already drained the radiator (again), pulled the thermostat housing and bolted my hose adapter onto the intake planning on flushing again. Going to run the water hose through the thermostat hole in the intake and let it flow out the top radiator hose and see what comes out. The last time I used the same hose in the intake but had the waterpump off, so just flowed it out the front and it flowed black for 10 mins or more, so it's got a buncha' something, but it DID clear completely then. I AM going to take the adapter back off and fill the engine with the Evapo Rust somebody suggested and let it sit overnight when it gets here. (tomorrow from O'Reilly's)

I did talk to my friend today who I bought it from and he said absolutely nothing wrong with the car when it was parked. He'd noticed a little green fungus (as he put it) around the original radiator and got scared to drive it, even though it wasn't losing coolant. Said it absolutely never ran hot. He ordered a brass/copper replacement but it would have required notching the shroud at the bottom so he didn't use it. Sometime later a mutual friend suggested he buy this aluminum replacement that's in the car now. He thinks the newest one came from South Carolina. (Griffin maybe???) So he gave me the original radiator with the car, but it's been in a box for many years. I'm very tempted to put it back in the car just to see if the replacement is the issue. The car is so original with all of the original drivetrain (L79) and no damage history or rust that I'm probably going to put a Dewitt's back in it anyway, but if I've got engine crap fouling the radiator I don't want to risk a new one.

[Mike T.]

Re: 65 L79 overheating, driving me nuts

Norris - Can you describe this 'black stuff' that's coming out? Is it granular like broken up rust particles?

[Dave P.]

Re: 65 L79 overheating, driving me nuts

I looked up Evap-o-rust chemical composition, but the ingredients are "trade secret". My experience has been that anything associated with dissolving Iron Oxide ("Rust") contains oxoholic (sp) and phosphoric acid. Phosphoric acid and aluminum are not compatible. At this juncture, it looks like 'saving' the existing radiator is not of concern, so using phosphoric in the engine block to clean it is probably ok, then.

The "black" is interesting. Usually, rusty blocks have "rusty" liquid in them, not "black". Phosphoric acid turns aluminum (and iron oxide) black. I wonder if someone prior to you has introduced a cleaner to the system that is attacking the aluminum radiator? My approach would be to eliminate the radiator. McGyver the outlet hose to the inlet hose. Keep your restriction washer, no thermostat. Then you can run it with your cleaning chemicals to circulate it under force of the pump, and let it marinate for periods of time (a day or two?) before draining. Repeat until the rinse water remains clear.

Remember that a raw iron surface will flash-rust almost immediately if left exposed to atmosphere. So be prepared to put the system back together and refill it as soon as possible after you deem it is "clean".

Don't forget about the heater core.

[Norris W.]

Re: 65 L79 overheating, driving me nuts

Norris - Can you describe this 'black stuff' that's coming out? Is it granular like broken up rust particles?

Just looks like black water. It IS 50/50 water anti freeze, but the green seems to be gone now. Under the thermostat is a different story. It looks almost like dirt. Maybe I'll get scrape with a screwdriver and post a picture.

[Mike T.]

Re: 65 L79 overheating, driving me nuts

And, since an L79 has an aluminum intake manifold, maybe that's another reason for caution using Evap-O-Rust?

[Mark E.]

Re: 65 L79 overheating, driving me nuts

And, since an L79 has an aluminum intake manifold, maybe that's another reason for caution using Evap-O-Rust?

I called CRC (manufacturer of Evap-O-Rust) tech support and they said it is safe with aluminum. On their website, you'll see a video demonstrating its use on a mid-year Corvette with an aluminum intake.

My first experience with this stuff was a couple of years ago on a 1993 LT1. I purchased it from the original owner with 13k miles but the coolant looked like it had never been changed... a dark rust color with a half inch of mud on the bottom of the overflow tank. After flushing and draining the system several times with water it drained clean, but a dark red film remained on the inside surface of the pressurized expansion tank (where the cap is located). So I tried this product. A LOT more stuff (rust, sediment, dirt) flushed out. Now the inside surfaces that I can see look like new.

To this day the coolant looks fresh, the overflow tank (where sediment tends to collect) remains clean and the pH tests good. I don't sell this stuff but want to share it's the best cooling system flush I've used. Plus it's not a harsh chemical like other flushes... I wouldn't wash my hands with it, but it doesn't irritate or burn on contact. CRC claims it's "non-toxic", whatever that means.

BTW, this car has several aluminum components- radiator, heads, w/p,...

A thought about the black color- a possible source can be a deteriorating hose.

[Patrick H.]

Re: 65 L79 overheating, driving me nuts

Have you drained the two plugs located at the bottom of the block, 1 on each side?

I would suggest that if you haven't, you remove them and be prepared to use a pick or small screwdriver to remove all the rust blocking the holes.

FYI, for the EvapoRust treatment I took and old water pump, plugged the radiator hose inlet, welded a thread on the end of the hub, and bypassed it back onto itself. I used a large drill to spin the pump and circulate the EvapoRust only through the engine without involving the radiator or heater core. It worked great.